1. Field of the Invention
The present invention relates to a liquid crystal device, liquid crystal driving device and method of driving the same, and electronic equipment.
2. Description of the Related Art
Alternating voltage driving such as polarity inversion driving every frame (hereinafter, briefly described as frame inversion driving), polarity inversion driving every line (hereinafter, briefly described as line inversion driving), and polarity inversion driving every dot (hereinafter, briefly described as dot inversion driving) is known at present as a driving system of an active matrix type liquid crystal device, particularly, a TFT type liquid crystal device. Further, in such driving systems, a driving system (hereinafter, briefly described as an opposite electrode inversion driving system) for applying the voltage of polarity reverse to that of a voltage applied to a pixel electrode to an opposite electrode is simultaneously adopted to reduce power consumption. In the following description, respective operations of the frame inversion driving and the line inversion driving using the opposite electrode inversion driving system will next be explained.
FIGS. 10A to 10C are views for explaining a conventional operation of the frame inversion driving. In the frame inversion driving, the voltage polarity of a data signal supplied to a data line is inverted every one frame period as shown in FIG. 10A. The voltage supplied to the data line is set to positive polarity +V in a frame period f1, and is set to negative polarity −V in a frame period f2. A voltage Vcom of the opposite electrode applied to the opposite electrode is also inverted every one frame period in synchronization with this voltage supplied to the data line. The voltage difference between the voltage V of this data signal and the voltage Vcom of the opposite electrode is applied to a liquid crystal. This is visually shown in FIG. 10B.
FIG. 10C shows a change in voltage applied to each pixel of a liquid crystal panel having e.g., 240 scanning lines with the passage of time. Selected periods for sequentially selecting the 240 scanning lines one by one are respectively defined as H1 to H240. Here, for convenience, ±5 V is uniformly applied to the liquid crystal as an example. The data signal of the positive polarity is applied in the frame period f1. When a scanning line 1 is selected in a selected period H1, the voltage of +5 V is applied to a pixel corresponding to the selected scanning line 1. When a scanning line 2 is selected in a selected period H2, the voltage of +5 V is similarly applied to a pixel corresponding to the selected scanning line 2.
At this time, as shown in FIG. 10A, the voltage Vcom of the opposite electrode is changed in synchronization with the beginning of the selected period H1 of the frame period f1. Therefore, a voltage caused by parasitic capacity, etc. is applied to the liquid crystal of pixels corresponding to scanning lines 2 to 240 during the selected period H1 in which the scanning line 1 is selected in the frame period f1.
As shown in FIG. 12, this parasitic capacity is a capacity CGD generated between a gate G and a drain D of a thin film transistor (TFT) 30, and a capacity CDS generated between the drain D and a source S. It is further considered that there is also an influence of wiring capacity floated in wiring.
In FIG. 10C, a voltage change caused by the parasitic capacity, etc. is set to ±0.1 V as one example. Accordingly, a voltage of +0.1 V caused by the parasitic capacity is added to −5 V as a voltage originally applied to the liquid crystal of a pixel corresponding to the scanning line 2 during the selected period H1 so that the voltage actually applied to this liquid crystal becomes −4.9 V. Similarly, a parasitic capacity value +0.1 V is added to −5 V as a voltage originally applied to the liquid crystal during the selected period H2 on a scanning line 3 selected in a selected period H3 so that the voltage actually applied to the liquid crystal becomes −4.9 V. Similarly, the voltage applied to the liquid crystal is changed by the parasitic capacity on each of scanning lines 4 to 240. At this time, the interval of a period for applying the voltage changed by the parasitic capacity to the liquid crystal is different every scanning line as shown in FIG. 10C, and this difference causes flicker, display irregularities due to luminance inclination in a vertical direction, etc.
FIGS. 11A to 11C are views for explaining an operation of the line inversion driving. In the line inversion driving, as shown in FIG. 11A, the voltage polarity of the data signal supplied to the data line is inverted every selected period for selecting each scanning line, and every one frame period. In FIG. 11A, a positive polarity voltage +V or a negative polarity voltage −V is applied to the pixel electrode every selected period. The voltage Vcom applied to the opposite electrode is also inverted in synchronization with this voltage applied to the pixel electrode. FIG. 11B visually shows a change in voltage applied to the liquid crystal every selected period for selecting the scanning line, and every one frame period.
FIG. 11C shows an operation in which the voltage polarity on an adjacent scanning line is further inverted in the frame inversion driving of FIG. 10C. A data signal voltage of +5 V is applied to the data line in the selected period H1 of the frame period f1 on the scanning line 1. A data signal voltage of −5 V is applied to the data line during the selected period H2 on the scanning line 2 selected in the selected period H2. In this case, polarity of the opposite electrode is inverted in the selected period H2 of the scanning line 1. Thus, a voltage of −0.1 V accumulated within the TFT 30 and wiring and caused by the parasitic capacity is added to a pixel so that the voltage becomes +4.9 V. Similarly, a voltage of ±0.1 V caused by the parasitic capacity is also added to +5 V or −5 V as a voltage originally applied to the liquid crystal on respective scanning lines 3 to 240. The voltage applied to the liquid crystal is changed by this voltage caused by the parasitic capacity. However, a period of this change becomes one line period and is not easily recognized as flicker so that image quality is improved in comparison with the frame inversion driving system. Further, the voltage polarity of the opposite electrode must be changed every selected period in the line inversion driving system. Therefore, it is necessary to synchronize timing for inverting the polarity of the opposite electrode with each selected period so that power consumption is increased in comparison with the frame inversion driving system.